1. Field of the Invention
This invention relates to apparatus for rapidly switching a magnetic field, and more particularly to an arrangement for rapidly switching a high frequency magnetic field.
2. Description of the Prior Art
Known domain transport stores include a plate, and in particular layer-shaped, storage medium, for example comprising magnetic garnet or orthoferrite material having domains which are magnetized perpendicular to the layer and in a magnetizing direction that is opposite to the magnetizing direction of the surroundings thereof and to a magnetic support field. The domains furthermore dispose of a periodic manipulation pattern to which individual elements of magnetizable material are applied, for example a layer of NiFe alloy, in rectangles, onto one layer surface. A magnetic field which turns at a high frequency parallel to the plane of the layers serves for the transport of the cylinder domain.
In a magnetic field which during operation is designed as a magnetic rotary field, parallel to the plane of the layer of the storage medium, the above-mentioned magnetic individual elements of the manipulation pattern create magnetic scatter fields under which effect cylindrical domains travel to energetically more favorable positions at the individual elements.
When rotating the magnetic rotary field in the plane of the layer these energy minimums disappear. In their place new ones are created at other points of the manipulation pattern to which the domains travel. In case of suitable geometry of the manipulation pattern the cylinder domains move, in case of a complete rotation of the magnetic rotary field, by one period of the manipulation pattern, which means that the domains advance by one storage space. In a continuously rotating magnetic field, the cylinder domains can be transported on paths which are prescribed by the manipulation pattern.
The magnetic rotary field which is required for the transport of the cylinder domains is, as is generally known, created in a pair of coils which are aligned in an orthogonal manner with respect to each other, whereby for energy considerations the coils are in each case designed to form resonant circuits which are controlled by a sine or cosine current, respectively.
In order to achieve an ideally rotating magnetic field in the working space of the coil, the phase position and the amplitude of the control currents have to be closely observed, this being the reason while the control is preferably carried out by means of a phase-coupled double generator with independent amplitude control for both outputs. This structure guarantees that the terminal point of the magnetic field vector accurately forms a circle.
If a resonant circuit is caused to oscillate, due to the activation of the high frequency generator, the full energy and, therefore, also the full magnetic field strength can only be achieved after many periods of oscillation, since the generator can supply the resonant circuit with its initial impedance only with a limited power, which, consequently, constitutes a restriction at the start. The conditions are similar when the generator is switched off. The increasing or decreasing of the current amplitudes has an exponential characteristic and is unsuitable in this form for the purpose of domain transport.
In a domain transport the full field amplitude should be available at the time the generator is switched on or during its activation, respectively, so that all cylinder domains start simultaneously.
Otherwise, due to the change of the opposite phase position of the individual cylinder domains, the information is obscured; the individual cylinder domains are transported, however, other cylinder domains are not transported to the next storage space since the critical threshold value of the field amplitude has not yet been exceeded. Similar facts also apply to the switching off of the rotary magnetic field, whereby the amplitude of the field is interrupted abruptly, or should at least be brought below a level at which the transport of the cylinder domains does not take place.
Therefore, it is essential to accelerate the switching on and off of the magnetic field in the form of a switch. A switch which is arranged in series in the resonant circuit and which would offer itself for the solution of this problem is, however, only acceptable as far as the basic factors are concerned. The losses caused by such a switch are excessive in the field of the required rotary field current.